Study On Generation And Characteristic Of High-order Harmonic In Laser Plasma Interation

Ultrashot laser pulse,as its name implies,is well known for its ultrashort duration and an extremely strong peak intensity.It exhibits extensive applications in physics,chemistry,biology and other interdisciplinary studies including femtochemisty,biophotonic imaging,and has achieved some remarkable achievements.When the ultrashort pulse containing only a few optical cycles,the carrier-envelope phase?CEP?is an important parameter and will greatly affect the nonlinear processes of laser-plasma interaction?LPI?.How CEP exerts its relevant characteristics in ultrashort laser pulse and how to control and use it has become an important topic in modern optical research.In this thesis,the PIC numerical simulation method is used to analyze the influence of CEP on the characteristics of high harmonic generation?HHG?caused by ultrashort laser pulses and plasma.The main contents are as follows:Using the LPIC++program to simulate LPI,three different mechanisms of attosecond pulse?AP?radiation can be observed:coherent wake emission?CWE?,relativistic oscillating mirror?ROM?,and coherent synchrotron emission?CSE?.When laser intensity₀a?27?1,CWE radiation can be generated in the plasma target;and when laser intensity₀a?29?1,it is possible to generate ROM and CSE,which is related to collective electrons on the plasma surface.Ultra-dense electron nanobunches can be formed at plasma surface that emit CSE.The resulting spectrum is much flatter and leads to the formation of a giant AP in the reflected radiation.The spectral characteristics of the higher harmonics generated by the ROM satisfy the power law with an exponent of-8/3.Therefore,in this paper,we introduce the differences and connections of these three mechanisms.CSE from electron nanobunches formed in relativistic LPI is a unique way of producing coherent extreme ultraviolet?XUV?and X-Ray radiation,which might be isolated AP or attosecond pulse train?APT?depending on various parameters of laser and plasma.The CSE is formed in the reflected beam as well as in the transmitted direction.In this paper,the AP generation mechanisms and their characteristics depending on the carrier envelope phase?CEP?are studied.By controlling CEP in the appropriate range,an isolated AP is produced.Effects other parameters on AP generation is also studied.The optimal combination of the plasma scale length L and the plasma thickness h with CEP is given.In the field of nonlinear optics,ultrafast optics is a subject that keeps pace with the times and is constantly being recognized and developed.In our work,the characteristics of collective electrons are discussed when an ultrashort laser pulse interacts of the appropriate range with dense plasma,and how the CEP affects HHG and the appropriate CEP range is required to the bright AP.We propose several schemes,which have certain research value to the development of ultrafast optics.